In a unit test, do you verify and assert?

Question

I am using Moq in my unit test project. Most unit test examples I've seen online end with someMock.VerifyAll(); I wonder if it is OK to assert after VerifyAll() . So for example,

//Arrange
var student = new Student{Id = 0, Name="John Doe", IsRegistered = false};
var studentRepository = new Mock<IStudentRepository>();
var studentService= new StudentService(studentRepository.Object);

//Act
studentService.Register(student);  //<-- student.IsRegistered = true now.

//Verify and assert
studentRepository.VerifyAll();
Assert.IsTrue(student.IsRegistered);

Any thought? Thank you.

Answer 1

No you should not use both together in most cases(there are always exceptions). The reason for that is you should be testing only one thing in your test for maintainability, readability and few other reasons. So it should be either Verify(VerifyAll) or Assert in your test and you name your tests accordingly.

Look at Roy Osherove's article about it:

http://osherove.com/blog/2005/4/3/a-unit-test-should-test-only-one-thing.html

VerifyAll is used to make sure certain methods are called and how many times. You use mocks for that.

Assert is used for verifying the result returned from the method you are testing. You use Stubs for that.

Martin fowler has a great article explaining the difference between mocks and stubs. If you understand it you will know the difference better.

http://martinfowler.com/articles/mocksArentStubs.html

UPDATE: example of mock vs stub using Moq as requested in the comment below. I have used Verify but you can use VerifyAll as well.

using Microsoft.VisualStudio.TestTools.UnitTesting;
using Moq;
... 

[TestClass]
public class UnitTest1
{
    /// <summary>
    /// Test using Mock to Verify that GetNameWithPrefix method calls 
    /// Repository GetName method once when Id is greater than Zero
    /// </summary>
    [TestMethod]
    public void GetNameWithPrefix_IdIsTwelve_GetNameCalledOnce()
    {
        // Arrange 
        var mockEntityRepository = new Mock<IEntityRepository>();
        mockEntityRepository.Setup(m => m.GetName(It.IsAny<int>()));

        var entity = new EntityClass(mockEntityRepository.Object);
        // Act 
        var name = entity.GetNameWithPrefix(12);
        // Assert
        mockEntityRepository.Verify(
            m => m.GetName(It.IsAny<int>()), Times.Once);
    }

    /// <summary>
    /// Test using Mock to Verify that GetNameWithPrefix method 
    /// doesn't calls Repository GetName method when Id is Zero
    /// </summary>
    [TestMethod]
    public void GetNameWithPrefix_IdIsZero_GetNameNeverCalled()
    {
        // Arrange 
        var mockEntityRepository = new Mock<IEntityRepository>();
        mockEntityRepository.Setup(m => m.GetName(It.IsAny<int>()));
        var entity = new EntityClass(mockEntityRepository.Object);
        // Act 
        var name = entity.GetNameWithPrefix(0);
        // Assert
        mockEntityRepository.Verify(
            m => m.GetName(It.IsAny<int>()), Times.Never);
    }

    /// <summary>
    /// Test using Stub to Verify that GetNameWithPrefix method
    /// returns Name with a Prefix
    /// </summary>
    [TestMethod]
    public void GetNameWithPrefix_IdIsTwelve_ReturnsNameWithPrefix()
    {
        // Arrange 
        var stubEntityRepository = new Mock<IEntityRepository>();
        stubEntityRepository.Setup(m => m.GetName(It.IsAny<int>()))
            .Returns("Stub");
        const string EXPECTED_NAME_WITH_PREFIX = "Mr. Stub";
        var entity = new EntityClass(stubEntityRepository.Object);
        // Act 
        var name = entity.GetNameWithPrefix(12);
        // Assert
        Assert.AreEqual(EXPECTED_NAME_WITH_PREFIX, name);
    }
}

public class EntityClass
{
    private IEntityRepository _entityRepository;
    public EntityClass(IEntityRepository entityRepository)
    {
        this._entityRepository = entityRepository;
    }
    public string Name { get; set; }
    public string GetNameWithPrefix(int id)
    {
        string name = string.Empty;
        if (id > 0)
        {
            name = this._entityRepository.GetName(id);
        }
        return "Mr. " + name;
    }
}

public interface IEntityRepository
{
    string GetName(int id);
}

public class EntityRepository:IEntityRepository
{
    public string GetName(int id)
    {
        // Code to connect to DB and get name based on Id
        return "NameFromDb";
    }
}

Answer 2

Yes you should call the assert.

VerifyAll() will assert that all SetUp() calls were actually called.

VerifyAll() will not confirm that your student object is registered. Because there are no SetUp() calls in your test case, I think VerifyAll() isn't verifying anything.

Answer 3

I would absolutely expect to see Verify and Assert used side-by-side within a unit test. Asserts are used to validate that properties of your system under test have been set correctly, whereas Verify is used to ensure that any dependencies that your system under test takes in have been called correctly. When using Moq I tend to err on the side of explicitly verifying a setup rather than using the VerifyAll catch-all. That way you can make the intent of the test much clearer.

I'm assuming in the code above that your call to the student repository returns a boolean to state that the student is registered? And you then set that value on the student object? In that case, there is a valuable setup that needs to be added, in which you are effectively saying that when the student repository method is called, it will return true. Then you Assert that student.IsRegistered is true to ensure that you have set the property correctly from the repository return value and you Verify that the repository method is called with the inputs that you are expecting.

Answer 4

There's nothing intrinsically wrong with both asserting and verifying in a mocking test, though assertions that depend on the actual methods being called are likely to fail, because the mock methods do not have the same effects as the real methods.

In your example it is probably fine, as only the repository is mocked, and the change of the student state is presumably done in the service.

Whether both verify and assert should be done in the same test is to a degree a matter of taste. Really the verify is checking that the proper calls to the repository are made, and the assert is checking that the proper change to the entity is made. As these are separate concerns, I'd put them in separate tests, but that may just be me.